The present invention relates to a photoelectric converting device, and in particular, to an improvement in the electrode structure of individual photoelectric conversion elements of an photoelectric converting device.
Generally, for a photoelectric converting device for use in image pickup devices the CCD (charged coupled device) type are widely known. This type, however, has a drawback in that overall image pickup device size cannot be made small due to the fact that it requires considerable optical path length owing to the necessity of the optical system to reduce the image to a proper extent as in ordinary cameras.
To solve such problem, a photoelectric converting device for dealing with real size images has been proposed recently. FIG. 1 shows an example of a photoelectric converting device of this type applied to the original reader of facsimile. In this figure, the original reader is accommodated in casings PA and PB, and consists of light sources 31 and 32, a lens array 20 which is an optical system for forming image, and an elongated photoelectric converting device 10. The photoelectric converting device 10 has its length corresponding to the width of the original OR to be placed on the casing PA, and its structure is such that the required number of divided electrodes 12 are provided on a substrate 11 on which a photoconductive layer 13 of amorphous silicon, selenium-Tellurium (Se-Te), organic semiconductor, or other suitable material is formed, and a light transmittable common electrode 14 is formed so as to cover the entire surface of the photoconductive layer 13. Each photoelectric conversion element (hereafter referred to simply as "element") which corresponds to a single picture element is comprised of a divided electrode 12, the photoconductive layer 13, and the common electrode 14, and the whole elements are formed to correspond to the full width of the original OR at a density of 8 elements/mm to 12 elements/mm, thus the photoelectric converting device 10 is constructed.
To achieve the reduction in the image pickup device size, an optical system capable of forming the original image on the photoelectric converting device in one to one correspondence, i.e., without enlargement and reduction, of image. The lens array 20 are provided for such an optical system. The lens array 20 is generally known as light converging fiber, typically structured by arranging light converging fiber 21 in a suitable holder at a density similar to or larger than that of aforementioned photoelectric conversion element, and disposed in such a manner that, as shown in FIG. 1, its optical axis is sabstantially vertical to the surface of the original OR set on the casing PA.
On both sides of the lens array 20 are disposed light sources 31 and 32, and light emitted through suitably provided slits 33 and 34 irradiates the original OR. That is, a glass plate 90 is provided in the casing PA corresponding to the width of the original OR, and the light emitted from the light sources 31 and 32 is cast as shown by arrows F1 in FIG. 1 on the original OR moving along the glass plate 90.
The light emitted from the light sources 31 and 32 is reflected at the surface of the original OR, enters and passes through the lens array 20 as shown by an arrow F2, and enters the photoelectric converting device 10 as shown in an arrow F3. Image reading scan of the original OR is performed by sequentially driving the elements of the photoelectric converting device 10.
For the light sources 31 and 32, a fluorescent lamps or LED arrays are employed, but the LED array involves a problem in the aspect of quantity of light.
FIG. 2 shows the quantity of light emission of the light source 31, 32 as measured in the longitudinal direction when a fluorescent lamp is used. As seen, when the quantity of light emission around the center of fluorescent lamp is taken as 100%, that of the end part LA, LB is around 80%.
On the other hand, since individual elements of the photoelectric converting device 10 are designed to have the same characteristic in photoelectric conversion, if the end portions LA, LB of the fluorescent lamps are used, sensing error would result. Accordingly, the light of the portion other than the portions LA and LB must be used, therefore, the construction must necessarily be such that the ends LA and LB of the light sources 31 and 32 protrude left and right. For example, for the photoelectric converting device 10 about 210 mm long, a fluorescent lamp as long as 320 mm is required.
To solve such problem, a method to process the output of the photoelectric converting device 10 electrically would be effective, but it requires special correction circuit.